1. Field of the Invention
This invention relates to a paper wrinkle preventing device of a rotary press, e.g., an offset rotary press for a newspaper having an offset printing portion in which two blankets are arranged so as to set their side edges to be adjacent to each other approximately at the center of a blanket cylinder in its axial direction and a printing operation can be simultaneously performed through these two blankets on web paper running in contact with these two blankets. More particularly, this invention relates to a paper wrinkle preventing device for dissolving angular deformation caused in the web paper approximately along a central position of the blanket cylinder on a downstream side of the offset printing portion, and preventing this angular deformation being wrinkled.
2. Description of the Background Art
It is known in offset printing that wet water reaches web paper through a lithographic plate and a blanket and the web paper is enlarged in width and longitudinal directions. Further, two blankets are arranged such that side edges of the blankets are adjacent to each other approximately at a center of the blanket cylinder in its axial direction. In the offset printing portion, the printing operation can be simultaneously performed through these two blankets on the web paper running in contact with these two blankets. In the offset printing portion, the lithographic plate corresponding to each of the blankets is mounted to a plate cylinder in a state in which side edges of the lithographic plate are slightly separated from each other. The printing operation is performed except for adjacent portions of the side edges of the two blankets.
Therefore, no wet water reaches portions of the web paper corresponding to the adjacent portions of the side edges of the two blankets during the printing operation through the lithographic plate and the blankets so that enlarging amounts of the web paper in these portions are small in comparison with the other paper portions. When the web paper printed by such an offset printing portion is pulled by a drag roller downstream from the offset printing portion, tension of each of the paper portions corresponding to the adjacent portions of the side edges of the two blankets in a running direction becomes larger than that of the other portions in the running direction since the enlarging amount of the web paper caused by the wet water is small. Accordingly, there is a case in which angular deformation is caused in this paper portion between the blanket cylinder and the drag roller downstream from this blanket cylinder.
In particular, the difference in enlarging amount provided by the wet water between the paper portions corresponding to the adjacent portions of the side edges of the above two blankets and the other paper portions is increased in the web paper sequentially continuously printed in plural offset printing portions. When this web paper is pulled by the drag roller downstream from a most downstream offset printing portion, it is confirmed that very clear narrow angular deformation is caused in the paper portions corresponding to the adjacent portions of the side edges of the two blankets between the blanket cylinder of the most downstream offset printing portion and the drag roller downstream from this blanket cylinder.
On the other hand, for example, a technique (prior art 1) described on pages 96 to 97 of "Newspaper Printing Handbook" (published by Japan Newspaper Association Corp. on Apr. 10, 1997) is known as the paper wrinkle preventing device. Namely, in this paper wrinkle preventing device, a reverse crown roller narrowed in a hand drum shape in a central portion of the roller and a crown roller thickened in a drum shape in a central portion of the roller are arranged in positions in which there is a fear that paper wrinkles are caused during a running path of the web paper. The reverse crown roller and the crown roller are constructed such that these rollers are simultaneously rotated in contact with the running web paper in its entire width. An outside diameter of each of the rollers gradually changed in left-right symmetry in an axial direction gives different tensions and sending directions to the center and both sides of the web paper running in contact with these rollers. Thus, the paper wrinkle preventing device prevents the web paper from being wrinkled by spreading the web paper in its width direction.
For example, a paper wrinkle preventing device having an expander roller shown in Japanese Published (Kokoku) Utility Model No. 62-32204 (prior art 2) and Japanese Laid-Open (Kokai) Patent No. 6-297605 (prior art 3) instead of the above reverse crown roller and the above crown roller is also known. This expander roller gives a sending-out direction directed to widen the width of the web paper in its entire width to the web paper running in contact with this expander roller by a peculiar movement or shape of a circumferential face of this expander roller in left-right symmetry with a longitudinal central position of this roller as a center. Thus, this paper wrinkle preventing device prevents the web paper from being wrinkled by spreading the web paper in its width direction.
The above conventional techniques have several problems to be solved. The angular deformation caused in the web paper offset-printed between the blanket cylinder of the above offset printing portion and the drag roller downstream from this blanket cylinder is left as flat wrinkles as it is when this web paper comes in contact with the drag roller as it is. Therefore, the quality of a product as a printed matter is reduced so that this product cannot be used as an article of commerce in a certain case.
Therefore, the applicant of this application made a trial for removing the paper wrinkles by a paper wrinkle removing device using the reverse crown roller, the crown roller and the expander roller disclosed in the above prior arts 1, 2 and 3.
However, when an entire face of the web paper having the above angular deformation simultaneously comes in contact with the rollers as entire face wrinkle removing rollers, the angular deformation becomes flat wrinkles. Further, no action for widening the web paper in the width direction by the wrinkle removing rollers reaches portions of the above flat wrinkles since strength of the web paper is reduced by wet water and the web paper is further enlarged in the width direction. Accordingly, no flat wrinkles can be removed from the web paper.